Correct me if I'm wrong;
My SS check is backed by present day FICA witholdings from workers
thus;
My check comes from a worker (I know, more than one ... KISS) from his last month's labor
If he contributed to FICA (the SS part) more than what I needed, the fed got to use it ... "general fund"
The federal government BORROWED it. It's actually part of the deficit, although they don't always make it obvious.
The problem with your original assertion: Just take it out of the general fund and put it back into an untouchable fund
It is in an "untouchable" fund. That's why Al Gore's "lock box" meme was laughable... it's always been that way.
The Social Security Trust fund is invested in the equivalent of US Treasury Bonds. They pay dividends that are equivalent to long-term US Treasury Bonds. You can look at the balance sheet in the report I cited above and see that: $98.2B on a balance of $2.76T in 2014.
That same annual report also shows that benefits paid exceeded taxes collected. That why the Trust Fund only increased $25B last year: because $73B was withdrawn to pay benefits. In the next few years, the Trust Fund balance will start to decrease as withdrawals increase.
Finally, I'll answer the question many people ask: why US Treasury Bonds? The truth is: until Obama screwed the pooch by threatening to suspend dividend payments, US Treasury Bonds were considered the safest investment in the world. But, consider what would have happened if the SSA had invested in equities or corporate bonds: it would have been crony capitalism at its worst. Congress would have never let the SSA choose investments based on value or safety -- there would have been all kinds of prohibitions and "earmarks" to pay off political favors.